Instrumentation amplifiers may be used in variety of industrial applications. An instrumentation amplifier may include a differential amplifier. A differential amplifier is a type of electronic amplifier that amplifies the difference between two input voltages but suppresses any voltage common to the two inputs. A differential amplifier may be an analog circuit with two inputs and one output in which the output is ideally proportional to the difference between the two voltages. An instrumentation amplifier may include a differential amplifier that includes input buffer amplifiers. These may reduce or eliminate the need for input impedance matching. Thus, the amplifier may be more suited for use in measurement and test equipment.
In many sensor applications, due to a complicated operating environment, a weak sensor output signal may be amplified. However, at the same time strong common mode signal variations like power line noise are to be rejected. An instrumentation amplifier may be configured to provide differential gains and high common mode rejection.
The common mode rejection ratio of an instrumentation amplifier is defined as input common mode signal variation divided by output signal variation over frequency. Poor common-mode rejection ratio can be caused by mismatch in resistor ratios and by mismatch in common mode gains of input op-amps. A classical architecture of instrumentation amplifier is to use three amplifiers with resistor feedback network.
The ideal common-mode gain of an instrumentation amplifier is zero. Common-mode gain can be caused by mismatch in resistor ratios and by mismatch in common mode gains of input op-amps. Instrumentation amplifiers can be built with individual op-amps and precision resistors, but are also available in integrated circuit form.